Jim, I think that you could contact Porter Music Box Company about
this.  They sell new 15.5" discs.

    Porter Music Box Company, Inc.
    U.S. Route 66, PO Box 424, Randolph, VT 05060
    (802) 728-9694 ~ (800) 635-1938 ~ FAX (802) 728-9699
    info@portermusicbox.com.geentroep (delete .geentroep when emailing)
    http://www.portermusicbox.com 

Ross Schacher
Marlboro, MA